Underwater excavation apparatus are known. The terms “mass flow” and “jet flow” are known, and understood in the art. Mass flow relates to flow at relatively low pressure and high volume, whereas jet flow relates to flow at relatively high pressure and low volume.
GB 2 297 777 A (Holandsche Beton Groep NV) discloses an underwater excavation apparatus comprising a hollow body having an inlet and an outlet, at least one pair of impellers coaxially displaced one from the other and rotatably mounted in the hollow body and means for driving the impellers of the/each pair in contrary rotating directions.
WO 98/027286 A (Ledingham Chalmers Trustee Company Limited) discloses an underwater excavation apparatus comprising a hollow body having at least two inlets and at least one outlet, at least one pair of impellers rotatably mounted in the hollow body, and means for driving the impellers, wherein the at least two inlets are substantially symmetrically disposed around an axis extending from the at least one outlet. Therein, preferably, the driving means cause the impellers to be driven in contra-rotating directions, and one of the impellers is provided within one of the inlets and another of the impellers is provided within another of the inlets.
GB 2 301 128 B (Ledingham Chalmers Trustee Company Limited) discloses an underwater excavation apparatus comprising an agitator device having mechanical disturbance means and fluid flow disturbance means which comprise a hollow drill bit having at least one hole provided in a side wall thereof, the drill bit providing a plurality of paddles disposed longitudinally and radially extending upon the drill bit and substantially equidistantly spaced one from another.
WO 2008/065360 A1 (Rotech Holding Limited) discloses an underwater excavation apparatus comprising a hollow body having at least one pair of inlets and at least one outlet, at least one pair of impellers rotatably mounted in the hollow body, means for driving the impellers, and at least one means for moving the underwater excavation apparatus, the at least one moving means being provided on or adjacent to the underwater excavation apparatus.
All of the above prior art underwater excavation apparatus are “mass flow” apparatus.
It is an object of at least one embodiment of at least one aspect of the present invention to seek to obviate or at least mitigate one or more problems in the prior art.
It is an object of at least one embodiment of at least one aspect of the present invention to seek to provide an improved underwater excavation apparatus.
It is an object of the least one embodiment of at least one aspect of the present invention to seek to provide an underwater excavation apparatus which is particularly useful in relatively shallow waters, e.g. 1 to 10 m, 1 to 2 m, or a few meters.